Thursday at a conference in Italy, chemist Steven Benner from the Westheimer Institute of Science and Technology in Gainesville, Fla., offered what he believes is evidence that in fact, "we are actually all Martians; that life started on Mars and came to Earth on a rock."

"Scientists have long wondered how atoms first came together to make up the three crucial molecular components of living organisms: RNA, DNA and proteins. ...

"Simply adding energy such as heat or light to the more basic organic molecules in the 'soup' does not generate RNA. Instead, it generates tar. RNA needs to be coaxed into shape by 'templating' atoms at the crystalline surfaces of minerals.

"The minerals most effective at templating RNA would have dissolved in the oceans of the early Earth, but would have been more abundant on Mars, according to Prof Benner.

"This could suggest that life started on the Red Planet before being transported to Earth on meteorites, argues Benner."

Benner, Space.com adds, thinks it's "lucky that we ended up here nevertheless, as certainly Earth has been the better of the two planets for sustaining life."

By the way, just how do Earth and Mars swap spit, as Adam puts it?

Back in March on Science Friday, Arizona State University cosmochemist Meenakshi Wadhwa was asked how rocks would get from there to here. "Large impacts ... are hitting Mars ... certainly in the past," she said. "And so there was a large impact on Mars sometime in the past and it ejected these pieces from Mars," which made their way through space to Earth.

What's more, she said, there could be pieces of other planets here on Earth.